whats the npk ratio your using now? and you dont need anything that strong for veg, the plant is still holding a lot of the fert in itself and now whatever your using now adding with whats already in the plant is causing the burn. whats the name of the fret you using both for veg and for bloom? also GoldenGraham84 is right get a 400W HPS conversion bulb it will help with yield and potency, and if you cant find a conversion bulb for your other unit just try to find a hps bulb with more blue in the spectrum.